The determination of antibodies against specific antigens (microbes) is of outstanding importance for making diagnoses. This is especially pertinent for antibodies of the immunoglobulin classes IgM and IgA, which are detectable in a patient's serum for a short period of time after an acute infection. The determination of specific IgM or IgA antibodies in serum specimens enables the diagnosis of acute infections.
The determination of antibodies which have been formed against specific microbes (antigens) is known. It is effected by fluoresence-, radio- or enzyme-immunoassays in such a way that an antigen is bound to an antibody and the binding reaction is determined by means of a labeled antibody. This method of operation, however, is subject to a series of deficiencies, which frequently yield incorrect results. Of importance in this context are the rheumatoid factors which react with aggregated IgG. In this case rheumatoid factor IgM is bound. Its determination, e.g. with labeled anti-IgM leads to wrong positive reactions. Wrong positive values are also obtained with anti-nucleic antibodies, since in general most commercially available antigens contain nucleic material. Furthermore many virus antigens contain Fc-receptors which likewise may lead to unspecific bondings. In addition it must be considered that especially with new-borns, which possess high concentrations of motherly IgG-concentrations, the binding of the specific IgM-antibody to the antigen may be blocked by the IgG-antibodies.
Incorrect results are also caused by the fact that labeled antibodies which are used in the known determination processes aggregate during their being labeled and form unspecific bondings with the rheumatoid factors which in the test method using labeled antibodies yield wrong positive values.